Can't open 1.4.7 world in Snapshots

I started useing the snapshops around 13w03a and my world,which has worked fine since 1.7 beta, crashes a few seconds after I opne it witht the snapshot. With every new snapshot it seems to stary open a little bit longer before crashing. I have included the crash report as an attachment. If you can resolve this problem thank you so much becuase I love this world. Also I have no modded blocks or modded items in chests.